14
M.L. Domeier
camoufl age grouper, E. polyphekadion (James et al. 1997 ) brown-marbled grouper,
E. fuscoguttatus , orange-spotted grouper, E. coioides , Malabar grouper, E. malabaricus , and giant grouper E. lanceolatus (Pomeroy et al. 2002 ) ]. Furthermore,
some species that form spawning aggregations have been observed spawning in the
fi eld outside of an aggregation (Randall and Randall 1963 ; Samoilys 1997 ; Krajewski
and Bonaldo 2005 ; Tuz-Sulub 2008 ) . Nassau grouper is a much studied species that
lends itself to this discussion; although Nassau grouper aggregations have been
documented throughout their range, they have never been observed to aggregate in
Florida, USA, or in the coastal areas of South America, regions where this species
occurs in relatively low abundance (Sadovy and Eklund 1999 , Yvonne Sadovy
unpublished data). Spawning aggregations for other species (e.g. snappers- Lutjanidae,
groupers) have been documented in Florida (Domeier et al. 1996 ; Coleman et al.
1996 ; Domeier 2004 ; Burton et al. 2005 ) so habitat may not be limiting the formation of a Nassau grouper spawning aggregation, leading to the likely conclusion that
Nassau grouper spawning aggregation formation is density dependent. If spawning
aggregations in general are density-dependent, this would tend to support the
hypothesis that aggregations require a local recruitment-based positive feedback
loop for them to form, as in the case of the bluehead wrasse, Thalassoma bifasciatum (see Chap. 12.14 ). If this were not the case we would expect individuals to be
instinctually seeking out the best spawning sites regardless of density. Whether or not
the formation of spawning aggregations is density-dependent is an important
question to address, and furthermore, is reproduction outside of an aggregation less
productive than spawning within an aggregation?
A widely cited early hypothesis suggested spawning sites were selected to
promote offshore dispersal of eggs to help developing larvae avoid predation by the
large number of planktivores found on coral reefs (Johannes 1978 ) . More recent
larval connectivity studies suggest, however, that the opposite may be occurring:
that local larval retention may be critical for recruitment success (e.g. Colin 1992 ;
Swearer et al. 1999 ; Taylor and Hellberg 2003 ; Paris and Cowen 2004 ; Domeier
2004 ; Almany et al. 2007 ) . These cited studies are just a few examples of a growing
body of work that support the hypothesis that the development of spawning
aggregations, and the selection of aggregation sites, is facilitated by the local
retention and recruitment of offspring. Following chapters of this book will explore
the concept of retention in much more detail (Chaps. 6 and 7 ).
Without knowing precisely how or why spawning aggregations form, it is impossible to understand the impacts and implications of heavy fi shing pressure upon a
species that aggregates to spawn. Certainly aggregations are exceptionally susceptible
to over exploitation, but does the process of spawning aggregation formation make the
recovery of an overfi shed stock much more diffi cult? Can spawning aggregations rapidly recover in the absence of fi shing pressure and the presence of high recruitment
from a distant source? Can spawning aggregations be created by heavy stock enhancement from hatchery reared, or transplanted individuals? Although fraught with problems,
stocking of an aggregating species into an area that no longer has a viable population
could address some of these questions although massive restocking of the large yellow
M.L. Domeier
camoufl age grouper, E. polyphekadion (James et al. 1997 ) brown-marbled grouper,
E. fuscoguttatus , orange-spotted grouper, E. coioides , Malabar grouper, E. malabaricus , and giant grouper E. lanceolatus (Pomeroy et al. 2002 ) ]. Furthermore,
some species that form spawning aggregations have been observed spawning in the
fi eld outside of an aggregation (Randall and Randall 1963 ; Samoilys 1997 ; Krajewski
and Bonaldo 2005 ; Tuz-Sulub 2008 ) . Nassau grouper is a much studied species that
lends itself to this discussion; although Nassau grouper aggregations have been
documented throughout their range, they have never been observed to aggregate in
Florida, USA, or in the coastal areas of South America, regions where this species
occurs in relatively low abundance (Sadovy and Eklund 1999 , Yvonne Sadovy
unpublished data). Spawning aggregations for other species (e.g. snappers- Lutjanidae,
groupers) have been documented in Florida (Domeier et al. 1996 ; Coleman et al.
1996 ; Domeier 2004 ; Burton et al. 2005 ) so habitat may not be limiting the formation of a Nassau grouper spawning aggregation, leading to the likely conclusion that
Nassau grouper spawning aggregation formation is density dependent. If spawning
aggregations in general are density-dependent, this would tend to support the
hypothesis that aggregations require a local recruitment-based positive feedback
loop for them to form, as in the case of the bluehead wrasse, Thalassoma bifasciatum (see Chap. 12.14 ). If this were not the case we would expect individuals to be
instinctually seeking out the best spawning sites regardless of density. Whether or not
the formation of spawning aggregations is density-dependent is an important
question to address, and furthermore, is reproduction outside of an aggregation less
productive than spawning within an aggregation?
A widely cited early hypothesis suggested spawning sites were selected to
promote offshore dispersal of eggs to help developing larvae avoid predation by the
large number of planktivores found on coral reefs (Johannes 1978 ) . More recent
larval connectivity studies suggest, however, that the opposite may be occurring:
that local larval retention may be critical for recruitment success (e.g. Colin 1992 ;
Swearer et al. 1999 ; Taylor and Hellberg 2003 ; Paris and Cowen 2004 ; Domeier
2004 ; Almany et al. 2007 ) . These cited studies are just a few examples of a growing
body of work that support the hypothesis that the development of spawning
aggregations, and the selection of aggregation sites, is facilitated by the local
retention and recruitment of offspring. Following chapters of this book will explore
the concept of retention in much more detail (Chaps. 6 and 7 ).
Without knowing precisely how or why spawning aggregations form, it is impossible to understand the impacts and implications of heavy fi shing pressure upon a
species that aggregates to spawn. Certainly aggregations are exceptionally susceptible
to over exploitation, but does the process of spawning aggregation formation make the
recovery of an overfi shed stock much more diffi cult? Can spawning aggregations rapidly recover in the absence of fi shing pressure and the presence of high recruitment
from a distant source? Can spawning aggregations be created by heavy stock enhancement from hatchery reared, or transplanted individuals? Although fraught with problems,
stocking of an aggregating species into an area that no longer has a viable population
could address some of these questions although massive restocking of the large yellow